INFLUENCE OF MULTIATOM INTERACTION ON THE SHAPES AND ENERGETICS OF 2-DIMENSIONAL HOMOEPITAXIAL CLUSTERS ON CLOSE-PACKED METALLIC SURFACES

We describe a scheme (BSM for ''bond saturation model'') for modeling the energetics of adatom clusters on close-packed metallic surfaces. I n the BSM, atoms interact via coordination dependent nearest-neighbor bonds. We show that the BSM yields a detailed understanding of the rel ationship between shape and energy for two-dimensional (2D) homoepitax ial adatom clusters on close-packed metallic surfaces. In particular, we advance a simple rule for predicting the binding energies of small clusters based on the moments of their coordination distributions, der ive a useful expression for the binding energy of a 2D cluster of arbi trary geometry, and study the role played by coordination dependent bo nding in determining step energies for adatom islands. Our analysis of step energies provides insight into why the two distinct types of mon atomic steps on Pt(111) have similar free energies as observed bu Mich ely and Comsa. While our numerical results are for Pt(111), we except our conclusions to hold for any chemically similar system.